Various types of substrates are coated with various types of coatings wherein the environment surrounding the substrate must be controlled to insure the quality of the coating. For example, automotive parts, aerospace parts, and appliance parts have various types of coatings applied thereto. The coatings, such as paints, top coats, and aqueous metallic slurries are applied to these parts.
For example, the U.S. Pat. No. 3,248,251 to Allen invention, discloses metal filled aqueous chromate/phosphate slurries. These slurries are commonly used on aerospace parts to impart a desired quality finish to the surface of the part. The quality of the finish is directly related to the environment about the part being coated.
The quality of any finish of an applied paint or other coating depends upon the cleanliness of the environment in which it is applied. With regard to waterborne materials, such as that described in the above mentioned Allen patent, moisture content of the environment can exert an even greater influence upon the coating. Therefore, it is critical to control the humidity of the environment in which the coating is being applied.
There are additional environmental concerns with regard to the application of various coatings. For example, chromate/phosphate slurries and aluminum filled chromate/phosphate coatings are widely used in aerospace applications. The chemical stability of the slurry composition and corrosion the resistance of the binder system of these coatings are a consequence of the presence of hexavalent chromium in the material. Hexavalent chromium is environmentally toxic and its levels must be controlled during application. This control is particularly critical when the coating films are deposited on parts by air spray techniques.
It is therefore desirable to provide a spray booth for applying coatings such as those discussed above wherein the spray booth controls the moisture content of the environment around the part being coated. It is further desirable for the spray booth to control the velocity flow of air therein. Controlling these environmental conditions facilitate reproducible deposition of uniform, tightly adherent, smooth coatings.
Prior art spray booths include large devices which recirculate humidified air in a closed loop to achieve humidity control. These devices were expensive, inefficient and poorly designed. These devices also recirculate air past the operator resulting in problems with Federal air/workplace regulations. It is therefore desirable to not only control temperature and humidity, but also comply with Federal regulations which limit the discharge of toxic, volatile, or other hazardous materials.
The U.S. Pat. No. 4,521,227 to Gerdes et al, issued Jun. 4, 1985, provides an improved air washer or scrubber for paint spray booths accommodating different air flows. The patent does not disclose any means for controlling the humidity within the paint spray booth.
The U.S. Pat. No. 4,590,847 to Hull, issued May 27, 1986, discloses an energy conservation upgrading for existing exhaust booths which provides an attachable air curtain supply make-up apparatus which delivers a substantial independent supply of outside air into an exhaust booth enclosure about the periphery of its inlet opening. This patent discloses no means for controlling the humidity within a spray booth.
The U.S. Pat. No. 4,616,594 to Itho, issued Oct. 14, 1986, discloses a painting booth including means for controlling temperature and humidity. Air having an appropriately controlled temperature and humidity is supplied into a zone in a painting chamber through which the object to painted is conveyed. This air supply is provided from ambient air passing through a humidity and temperature control apparatus directly over the substrate to be painted while air from a second source flows outside the first stream of air having the controlled temperature and humidity. The Itho patent does not disclose a totally controlled isolated environment within a second controlled environment wherein the second controlled environment is utilized to regulate the temperature and humidity of the contained controlled environment.
The present invention provides a controlled environment which maintains constant moisture content in the spray booth while also controlling velocity and flow of air in the environment immediately surrounding the part being coated, thus facilitating the reproducible deposition of the coatings. The device further limits the discharge of hazardous materials outside of the spray facility. Further, the present invention can be adapted for various coating processes.